Exposure of a foreign material to body fluids sometimes produces adverse physiological reactions. This is true in particular for medical devices, e.g., of metal or plastic, that require contact with blood. Adverse reactions include the formation of thrombus, i.e., clotting on the exposed surfaces of the device which can cause blockage of tubular devices such as catheters or cause emboli to form which can enter the blood stream and block smaller blood vessels, leading to organ damage or stroke. To reduce the complications arising from thrombus formation an anticoagulant such as heparin is sometimes administered to prevent clot formation in or on the device. Heparin coatings have also been applied to polymer medical device substrates.
In addition to inhibiting clot formation, it is useful to inhibit other adverse reactions to medical devices such as cell proliferation which can lead to hyperplasia, occulsion of blood vessels, platelet aggregation, rejection of artificial organs, infection, calcification and to enhance tissue growth function.